Commutator



July 14, 1953 P. A. MARSALl 2,645,732

COMMUTATOR Filed March 25, 195s 2 sheets-sneer 1 JNI/ENTOR.

:.10 PAUL AMARSAL NORME? y July 14, 1953 P. A. MARsAL 2,645,732

PAUL A.MARsAL BY gi Lm ATTORNEY Patented July 14, 1953 COMMU'IATOR Paul A. Marsal, Rocky River, Ohio, assignor to Union Carbide and Carbon Corporation, a corporation of New York Application March Z3, 1953, Serial No. 343,931l

3 Claims.

This invention relates to improvements in the construction of commutators for electric motors and generators. More particularly, it relates to improvemense in the construction of commutators for small, high-speed, 4 electric motors wherein the commutator segments are rigidly positioned in a mass of molded insulating material.

Present commutatore of this type employ a metal segment material. As good electrical conductivity is required of the segments, copper is most frequently used. However= metal segment materials do not form a sufficiently strong bond with the molded insulating material to withstand the forces exerted thereon under operating conditions which may include a commutator speed as high as 15,000 R. P. lV. and a temperature as highl as 200 C. For this reason, the segments, or the cylindrical body oi segment material from which the segments are subsequently out, are provided with inwardly projecting nns, ribs, or tongues which are of dove-tail or other mechanical keying coniiguration, and extended radially into the mass of molded insulating material in order to securely fasten the segments thereto.

While lmechanical keying is reasonably eiective in lsecuring the commutator segments, it has several disadvantages. It requires machining' the tongues or other mechanical locking device. This not only adds considerable expense to the construction cost, but constitutes a difficult operation Where the machining must be done on the inner surface of a small cylindrical body of segment material against which the insulating mass is to be molded. This machining operation increases in difliculty as the commutatcr decreases in size or the number of segments increase. In addition, any machining must be done accurately because a poor segment weight distribution is very detrimental to commutator life at high speeds.

One object of this invention is to provide a commutator of the type described wherein no special mechanical coniiguration is necessary to secure the segments to the mass of insulating material, the segments being secured solely by the bond between the segment material and the insulating material.

An additional object is to provide a commutator which, while e'lcient and durable in use, is simple and economical to construct.

This invention is based on the discovery that when carbon is used as a segment material and an epoxy resin is employed as an insulating malll) terial, the resin may be molded against the carbon by the application of heat and pressure to form a joint which is mechanically and thermally stable, even under high-speed commutator operating conditions, without any mechanical keying.

In the drawings:

Fig. l is a perspective view of a cylindrical tube of carbon commutator segment material.

Figs. 2 and 2A are perspective views ofthe two types of metal bushings ysuitable for use in the proposed commutator,

Fig. 3 is a perspective View of the cylindrical body of carbon commutator segment material with the metal bushing coaXially aligned therein and the interstice lledwith a mass of molded, heat-hardened, insulating resin.

Fig. 4 is a perspective view of the assembly of Fig. 3 with the commutator segments cut therein.

Fig. 5 is an end view of the commutator shown in Fig. 4 with a portion thereof cut away.

Fig. 6 is a section on lines 6-6 of Fig. 5.

Fig. 7Y is a view of one type of terminal which may be employed in soldering leads to the individual segments.

Fig. 3 is a view, parts being broken away, showing the parts of a modified commutator assembled in preparation for the introduction ci the resin into the opening around the bushing.

' Fig. 9 is a sectional view, taken along the line 9 9 shown in Fig. l0, of the modified commutator. Y y

Fig. 10 is an end vieyzgparts being broken away along the line Ill-Ill shown in Fig. 9, of the modied commutator.

Fig. 11 is a perspective view of the fully assembled modiiied commutator.

Referring to the drawings, a cylindrical carbon tube lll of suitable diameter is cut to the desired length of the proposed commutator segments. Preferably, the carbon tube has one side longitudinally slit Il to enable it to be` compressed slightly while inserting it into ya mold in preparation for a subsequent molding operation. A metal Ibushing i2 or lZA is provided for insertion within the carbon tube I0 in coaxial alignment therewith. Flanges i3 or ISA or other suitable irregularities on the external surface of the bushings i2 and IZA serve to securely lock the bushing in the mass of insulating mateial which is subsequently molded thereabout.

With the bushing l2 coaXially aligned within the cylindrical carbon tube lil, the assembly is secured within a mold and the space between the bushing and carbon tube illed with insulating material |4. The insulating material employed in this invention is an epoxy resin, which may be combined with the usual amount of illlers, such as asbestos, paper, carbon and the like, if desired, the amount and technique of employing illlers being well known in the resin molding art. rThe insulating mass |4 is subjected to the action of a suitable hardening agent or sufficient heat and pressure to convert it to an infusible state.

The term epoxy resin as used in the art as well as in this specification and appended claims designates a heat hardenable resin which is essentially a polyether derivative of a polyhydric phenol containing epoxy groups (and free from functional groups other than epoxy and hydroxyl). The rate at which these resins harden when heated can be favorably increased by the addition of organic or inorganic alkaline catalysts, such as amines, and hydroxides, for example, sodium hydroxide.` The epoxy resins described in the following patents are examples of those from which the commutator of the invention can be fabricated: 2,444,333, Castan; 2,521,911, Greenlee; 2,521,912, Greenlee; and 2,506,486, Bender et al. The p-referred resin is a diglycidyl ether of dihydroxydiphenyldimethylmethane which is amber colored and has a viscosity of between 60 and 100 poises.

After removal from the mold, the unit is cut longitudinally to form the commutator segments I6, separated by the slots |5. If the carbon tube il] was cut initially (I I) to facilitate insertion in the mold, one slot |5 should be made to coincide with this cut. A carbon commutator thus made is very strong and the segments are securely fastened to the epoxy resin insulating material despite the absence of mechanical keying.

Since electrical leads can not be attached to the carbon segments readily, some provision must be made for fastening the leads thereto. One method is to cut notches 2| in one end of the cylindrical carbon tube |0 prior to assembling the commutator, one such notch being provided for each proposed segment lead. Each notch area is coated with molybdic acid which is allowed to dry and then ilred in a reducing atmosphere at about 1200 C. for about one minute. The molybdic carbide formed is readily wet by a solderwettable metal, preferably copper 22. This copper coated notch provides an excellent terminal for soldering leads.

In the modified commutator shown in Figs. 8, 9, l0, and l1, a metal flange 3|, preferably of brass, is provided as a means for connecting the lead wires and the commutator segments 32. To

secure good electrical contact between the ila-nge 3| and the carbon segments 32, the flange 3| is attached to or made integral with a thin metal tube 33, preferably of brass, which fits snugly into the carbon tube 34. In the preferred embodiment of the invention, an annular groove 35 is cut in the inner surface of the carbon tube 34, and the metal tube 33 is extended along the carbon tube 34 covering, at least in part, the annular groove 35. The metal tube 33, being thin and of a malleable metal in the preferred embodiment, is made to conform to the annular groove 35 in the carbon tube 34 when the insulating, epoxy resin 33 is introduced under pressure into the interstices between the bushing 31 and the carbon tube 34 and metal tube 33. This serves to lock the metal tube 33 and flange 3| in place and insure good electrical contact between the flange 3| and carbon tube 34. When the commutator segments 32 are cut, as shown in Fig. ll, the cut portions or segments 38 of the flange 3| provide a surface which can be wet by solder and to which leads may be conveniently attached.

A joint of sufficient strength for most commutating conditions is obtained by hardening the epoxy resin, as described, against the relatively smooth inner surface of the carbon tube. If additional strength is required, annular grooves 33 may be provided in the carbon tube 34. These grooves increase the area of contact between the carbon tube and the resin, thus increasing the strength of the joint.

What is claimed is:

1. A commutator comprising a bushing, an insulating core of a heat-hardened epoxy resin, and carbon commutator segments, one end of said segments being disposed in electrical contact with a conductor capable of being wet by solder and adapted to receive electrical leads.

2. A commutator comprising a bushing, an insulating core of a heat-hardened epoxy resin, and carbon commutator segments, at least a portion of one end of each commutator segment being coated with molybdic carbide on which a coating of solder-wettable metal is superimposed.

3. A commutator comprising a bushing, an insulating core of a heat-hardened epoxy resin, and carbon commutator segments, one end of said segments being held in electrical contact with metal segments by said insulating core, said metal segments presenting a suitable surface for the attachment of leads.

PAUL A. MARSAL.

No references cited. 

1. A COMMUTATOR COMPRISING A BUSHING, AN INSULATING CORE OF A HEAT-HARDENED EPOXY RESIN, AND CARBON COMMUTATOR SEGMENTS, ONE END OF SID SEGMENTS BEING DISPOSED IN ELECTRICAL CONTACT WITH 